Comer appears to be a second lieutenant. He was from Barbour County, Alabama. This is a copy of a photo now in the Southern Historical Collections at the University of North Carolina at Chapel Hill: http://www.lib.unc.edu/mss/inv/c/Comer_Family.html

From a handwritten note on the back of the postcard (original spelling retained): "Aunt Nancy, sister of John Bell who was bought by W. R. King to keepe them from being separated in Washington DC. John was his boddy servant. To whome he left 1000 $...